This invention relates to a high power-to-weight electromotive device capable of use as a motor, alternator or generator. Electromotive devices are known for use both in transforming electrical energy into mechanical power and transforming mechanical power into electrical energy. In both cases, the energy or power producing capability results from relative movement between a magnetic field and electrically conductive elements.
Lightweight motor, alternator and generator devices are well known and some are capable of operation at high speeds. However, many such devices are not capable of producing high power at high speeds. For example, high power density devices of 0.6 horsepower per pound of weight are known to be useful for periods of intermittent operation, but such devices are incapable of continuous operation at high power densities in excess of 1 horsepower per pound. Also prior high power electromotive devices have not been capable of simultaneous high speed and high torque operation, nor have they provided efficiency of operation.
Many of the problems associated with achieving a high power-to-weight ratio electromotive device have been addressed by U.S. Pat. No. 4,900,965. The '965 patent discloses an electromotive device with a high power density per unit weight effected by utilization of an armature assembly having a large diameter-fin cross section speculation ratio. This structure of the '965 patent results in low opposing induced currents, as well as low eddy currents, to enable operation of the electromotive device at high efficiency with maintainable high torque during high speed operation.
The '965 patent provides for minimal hysteresis or eddy current losses by providing a flux path through stationary iron. This design led to an improvement over conventional motors which suffer such eddy current losses due to the fact that the iron through which the flux path travels is moving. Since the torque of the motor is proportional to the flux, any reduction in the flux will result in decreased torque. In a typical electric motor, the torque will fall off rapidly with increasing speed. The eddy current losses in the copper conductors and armature bars are associated with the windings or copper and are caused by cross leakage between the bars (made worse by radially long bars) and direct exposure of the copper to the magnetic field, and over saturation of the armature bars due to an excess amount of permanent magnet material.
The '965 patent provides a device which minimizes those losses. Losses associated with bar to bar cross leakage are reduced by designing the '965 device to incorporate radially short armature bars. Losses induced by the copper being directly exposed to the magnetic field is solved by the '965 patent through the use of an I-shaped armature bar acting as a shield to the magnetic field. Finally, losses caused by oversaturation of the armature bars are solved by the '965 patent by designing the amount of permanent magnet material such that the bars just approach saturation. The design of the '965 device, however, necessitates that the flux travel through at least four air gaps, a design which has led to problems as a result of air gap reluctance. It has been found that to maintain useful flux density in spite of the air gap reluctance, the magnets must be thickened radially. However, such a modification enlarges the diameter of the motor, increases the weight of the motor, and increases the cost of the motor, all of which are contrary to the desire to have a lightweight motor. Since the torque levels of the motor are proportional to the amount of useful flux, less useful flux will result in reduced motor torque and higher current draw at higher speeds for the motor. Therefore, it is still an objective to design a high powered, lightweight motor having high torque levels and increased useful flux.
Another high power-to-weight ratio electromotive device has been addressed by a dispersed conductor electromagnetic device which is the subject of U.S. Pat. No. 5,004,944. The '944 design utilizes a straight-sided armature bar of powdered iron which allows full exposure of the copper windings to the magnetic field. The powdered iron does not have the flux-carrying ability that other embodiments such as silicone iron does. To minimize the eddy current effect, the '944 patent utilizes extremely fine wire with its windings. The armature bars are fabricated from powdered iron to maximize the amount of flux traveling through what would otherwise be a very large air gap.
The '944 approach has been proven undesirable in terms of power-in versus power-out due to the resistance characteristics of the fine wire. This resistance characteristic causes significant energy losses in the form of heat at higher operating levels which translates into lost power and efficiency. In addition, the straight-sided armature bars do not easily lend themselves to standard production automatic winding techniques as the coils tend to slip outward from between the bars. Thus, other winding techniques must be utilized.
The power loss in the '944 patent due to fine wire resistance is again compensated for by increasing the amount of permanent magnet material beyond the saturation level of the iron bars. Aside from the costs of additional material, however, the bulk of this additional flux goes to the copper winding in the form of eddy current loss and is dispersed, leaving very little gain in power for the additional material investment.
While the preceding and other various arrangements have been designed with the objective of achieving a high power-to-weight ratio electromotive device, they have not been completely successful.
Thus, it is primary objective of this invention to provide an electromotive device which achieves a high power-to-weight ratio by dispersing the electromotive windings to minimize eddy currents within the coils.
It is a further object of this invention to provide an electromotive device which achieves a high power-to-weight ratio by dispersing the electromagnetic field core pieces to minimize eddy currents.
It is a still further objective of this invention to provide an electromotive device which achieves a high power-to-weight ratio by dispersing the electromotive windings to minimize eddy currents within the coils and dispersing the electromagnetic field core pieces to minimize eddy currents generally.
It is another objective of this invention to provide an electromotive device which achieves a high power-to-weight ratio by shielding the electromotive windings with field core piece extensions to minimize eddy current within the coils.
It is still another object of this invention to provide an improved electromotive device capable of use as a highly efficient motor, alternator, or generator.
It is still another object of this invention to provide an improved electromotive device that is capable of continuous operation at high power densities in excess of one horsepower per pound.
It is still another object of this invention to provide an improved electromotive device having an optimum thickness armature assembly which represents a balance among the effects of heat transfer to the cooling medium, heat production from resistance heating and other sources, and torque production.
It is still another object of this invention to provide an electromotive device of simple design having an integrated flux return path.
It is still another object of this invention to build an electromotive device having the maximum flux in the iron cores and incorporating a built-in return path in these cores, thus eliminating the need for a separate return path.
A final object of this invention is to use the core stators having integral flux return paths in curvilinear sections up to 360.degree. to drive, without limitation, devices such as rim mounted magnets on fans, propellers and impellers.
The foregoing and other objectives will become apparent to one skilled in the art as the description proceeds. The invention resides in the novel construction, combination and arrangement of parts substantially as described and illustrated in the specification and drawings of this patent application, and more particularly as defined by the appended claims. It is understood that changes in the precise embodiments of the disclosed invention are meant to be included as within the scope of the claims. The description of the preferred embodiment is intended to be illustrative and is not intended to be limiting upon the scope of the claims.